Photonics SpectraMay 2018
SYDNEY and ADELAIDE, Australia — Researchers have demonstrated an enhanced magnetic dipole source in the terahertz frequency range. Developing a terahertz magnetic source is a necessary step to harness the magnetic nature of light for terahertz-driven devices.

Collaborating scientists from the University of New South Wales, the University of Adelaide, the University of South Australia and Australian National University showed how a magnetic terahertz source could be produced. The team used a simple setup: Terahertz radiation was directed through a narrow hole next to a fiber of a subwavelength diameter, i.e., a fiber with a smaller diameter than the radiation wavelength. The fiber was made of glass, a material that supports a circulating electric field.

Electrical and optical engineers in Australia have designed a novel platform that could tailor telecommunication and optical transmissions. They experimentally demonstrated their system using a new transmission wavelength with a higher bandwidth capacity than those currently used in wireless communication. These experiments could open up new horizons in communication and photonics technology. Here, a schematic of the problem: aperture in a metallic screen with a dielectric fiber placed on top acting as a magnetic dipole emitter when excited by a wave incident on the aperture. Courtesy of Andrey E. Miroshnichenko.By placing the fiber next to the hole in a metal screen, the team found that the radiation power could be enhanced by more than one order of magnitude. The team attributed this enhancement to the excitation of the Mie-type/WGM resonances formed in the cross section of the microfiber.

The team believes that this experiment is the first proof-of-concept of radiation enhancement of a magnetic dipole source in the vicinity of a subwavelength fiber. It is also believed to be the first observation of the Purcell effect for a magnetic dipole source in the terahertz frequency range.

Researchers said that this hybrid platform of aperture and fiber could be further expanded into an array configuration, opening up a new type of hybrid metasurface for manipulating terahertz and higher frequency radiation.

Using guided modes of the fiber could lead to new avenues for developing integrated devices. Terahertz radiation provides a focused signal that could improve the efficiency of communication stations and reduce power consumption of mobile towers.

“I think moving into terahertz frequencies will be the future of wireless communications,” said researcher Shaghik Atakaramians.

The coupled magnetic dipole and optical fiber system could be scaled down to optical frequencies, which could facilitate development of integrated nanophotonic devices such as nanoantennas or lasers on fibers. The source-fiber platform could be tweaked to alter the enhancement of the terahertz transmissions.

“We could define the type of response we were getting from the system by changing the relative orientation of the source and fiber,” Atakaramians said.

The team emphasized that the ability to selectively enhance radiation is not limited to terahertz wavelengths.

“The conceptual significance here is applicable to the entire electromagnetic spectrum and atomic radiation sources,” said Shahraam Afshar, the research director.